The present invention relates to an intake air flow measuring apparatus for an engine, and more particularly to such an apparatus which uses a Karman vortex air flowmeter.
In a conventional electronically controlled fuel injection internal combustion engine, one way of measuring intake air flow into the engine is a digital Karman vortex air flowmeter. The intake air flow measured by the Karman flow meter has been used to control a fuel injector valve to control fuel injection quantity in accordance with the intake air flow. In this case, the Karman vortex air flowmeter includes a pair of hot-wire vortex detectors which produce vortex signals which are then shaped by a waveform shaper. The average number of the shaped Karman vortex signal pulses falling within 720.degree. of crank angle rotation is calculated by reference to four successive 180.degree. crank angle signal pulses. The frequency of the Karman vortex signal is calculated from the number of the Karman vortex signal pulse and engine speed.
However, under certain engine operating conditions, particularly when the throttle valve is fully opened and therefore relatively great fluctuations of intake air flow occur, the calculated intake air flow has been greater than the actual intake air due to time delays inherent in the digital nature of the flowmeter.